Will Adult Feeding Damage Rule out Introducing Mecysolobus Erro Against Buddleia Into New Zealand?
Total Page：16
File Type：pdf, Size：1020Kb
Seventeenth Australasian Weeds Conference Will adult feeding damage rule out introducing Mecysolobus erro against buddleia into New Zealand? Toni M. Withers, Belinda A. Gresham and Michelle C. Watson Scion, Private Bag 3020, Rotorua 3046, New Zealand Corresponding author: [email protected] Summary We are evaluating the potential benefits of which appears to peak each autumn (Watson et al. a second biological control agent for buddleia (Buddle- 2009). ja davidii Franch.) in New Zealand in addition to the buddleia leaf weevil, Cleopus japonicus Wingelmüller. MATERIALS AND METHODS Adult Mecysolobus erro (Pascoe) feed on the terminal Mecysolobus erro was imported from China into stem and fleshy leaf midribs and petioles of buddleia, the Scion Invertebrate Quarantine and Containment while the larvae are stem borers, causing stem collapse. Facility in 1999. No-choice oviposition and feeding No-choice host specificity testing of adults in China assays were conducted using 30 adult pairs of the predicted the insect was host specific to Buddleja spe- second generation of the laboratory colony that had cies. However, no-choice testing within containment in been over-wintered at 10°C. Pairs were transferred New Zealand revealed significant adult feeding upon in spring to a quarantine room maintained at 21°C terminal shoots of non-target Scrophulariaceae, e.g. and 70% RH and a 14:10 h L:D cycle, and each pair Scrophularia auriculata L. and Verbascum thapsus L., provided with one soft, current season’s B. davidii and some less closely related native plants, Parahebe stem, that was then changed three times a week. Plant hookeriana (Walp.) W.R.B.Oliv. and Hebe salicifolia stems were presented to each pair with their cut bases (L.) Lam. The colony of M. erro has since died out and sitting in a water-filled 150 mL glass conical flask. The it may not be economically justifiable to reintroduce it stem was firmly wrapped with a paper towel where it to undertake the multiple choice testing that would be entered the neck of the flask to act as a bung. A 800 necessary to try and determine what the adult weevil’s mm high sheet of mylar was rolled into a cylindrical plant feeding preferences might be in the field. tube and placed over the flask, and covered at the top Keywords Buddleja davidii, Mecysolobus erro, with fine nylon mesh. Where possible, host plant stems buddleia, host specificity testing, Scrophulariaceae. for testing were presented as rooted cuttings with the roots submerged in the water, or as potted plants with INTRODUCTION the mylar tube sunk 1 cm deep into the potting mix. Buddleia (Buddleja davidii Franch.) is a significant Pairs consistently ovipositing for 3 weeks were weed of forestry plantations and natural areas of New selected for the host trials. Pairs were re-used sequen- Zealand. The buddleia leaf weevil, Cleopus japonicus tially throughout the testing, but were rotated between Wingelmüller, was released in New Zealand in 2006 control and non-target plant species, with at least 1 as a biological control agent. We are evaluating the week between non-target tests. Pairs were excluded if potential benefits of a second agent, Mecysolobus they failed to oviposit on B. davidii during that week. erro (Pascoe) (Coleoptera: Curculionidae). Adult M. For each host test, each pair was given access to erro feed on the terminal stem and fleshy leaf midribs two stems of the test plant for 2–3 days, after which and petioles of buddleia (Zhou et al. 2000). Eggs are time each stem was scored for feeding damage: oviposited singly into intricately formed chambers 0 = no feeding evident near the tips of young stems. Females often form more 1 = very few feeding scars, than one chamber per stem, but not all contain an egg. 2 = some feeding scars, but less than would normally Larvae are stem borers that feed initially within the occur on B. davidii oviposition chamber, then tunnel downwards, often 3 = feeding scars similar to that on B. davidii during completely excavating the lower part of the stem the same period. causing entire stems to collapse and die. Larvae grow The number of eggs deposited within the stem was up to 13 mm long. recorded by carefully peeling back the outer layer of Information gathered to date on M. erro suggests the stem with a scalpel, then replacing it. All stems they have potential to be very damaging to the spring containing eggs were labelled and transferred into and summer growth of buddleia. Such attributes will water-filled vials and inspected weekly to ascertain if complement the damage achievable by C. japonicus, larvae were capable of development. Control stems 360 Seventeenth Australasian Weeds Conference were held with their bases in water-filled vials for Therefore, we can now add M. erro to the list of insects 3 weeks, and then those showing evidence of larval that find Scrophularia, Verbascum and Buddleja spp. feeding (frass and feeding holes) transferred to sealed equally palatable. labelled plastic bags until adult emergence (Gresham Geniostoma ligustrifolium is the only endemic et al. 2002). representative of the family Loganiaceae, and it was not a palatable plant to M. erro. The most surprising Host plants for testing Buddleja has in the past had result was the extent of the adult feeding damage to its own family Buddlejaceae, but is now considered the New Zealand native plants Parahebe hookeriana to be in the Scrophulariaceae. New Zealand has no and Hebe salicifolia. These genera were previously native Buddleja species. The relative palatability of placed within the Scrophulariaceae, which justified eight exotic Buddleja spp. was tested. Eight species of their inclusion in the draft host plant testing list drawn indigenous plants that either were or still are classified up in the 1990s. But these large genera have now been within the Scrophulariaceae and a further seven exotic defined as their own clade of Plantaginaceae placing species were also tested. Three exotic plant species them more distant from the Buddlejaceae (Stevens from other families that commonly grow in association 2001). Feeding damage consisted of multiple holes with B. davidii in New Zealand were also tested, as within the terminal buds, stems, leaf bases and petioles was the host plant of one other Mecysolobus sp. (Table on the backs of the leaves, resulting in stems wilting 1). In all cases, the fleshiest stems available, ideally and collapsing completely. Such damage could provide with diameters of at least 7 mm, were preferentially an entry point for pathogens and would undoubtedly chosen for the testing. reduce the reproductive capacity of the plant as flower spikes are produced only on terminal buds. Data analysis Statistical comparisons of feeding The reason for such high feeding damage to the scores and numbers of eggs laid were made using a native plants P. hookeriana and H. salicifolia remains Generalized Linear Model procedure using square-root unknown. However the relative palatability shown plus ½ transformed data to manage zero counts. Means under no-choice conditions was high enough that were separated by Tukey Test (Minitab 15). multiple choice testing on a high proportion of the species in these extensive genera is now required to RESULTS AND DISCUSSION ascertain the likelihood of damage in the field. In the Adult feeding damage Mecysolobus erro adults absence of such data, it is unlikely the risk posed to created the highest feeding damage upon Buddleja the native flora by the introduction of M. erro would spp. (Table 1) and there was a significant difference be considered justifiable. according to host plant (GLM: F = 28.04, P <0.0001). Notably, there was no significant difference in the ex- Adult oviposition The mean number of eggs laid by tent of feeding damage to the Buddleja spp. of South M. erro was highest on some Buddleja spp. (Table 1) African and South American origin, B. auriculata, B. and there was a significant difference in mean eggs laid salviifolia (classified into Section Chilianthus of the according to host plant (GLM: F = 7.46, P <0.0001). genus) and B. globosa, compared to those of South The only other plant species that was accepted for East Asian origin, B. davidii, B. madagascariensis oviposition was the exotic weed V. thapsus with a (classified into Section Nicodema of the genus) and mean of 1.2 eggs laid. The acceptability of plants for B. alterniflora. oviposition, based on this no-choice test data, strongly In the less-closely related tribes of Scrophular- suggests that no self-sustaining populations of M. erro iaceae, the highest adult feeding damage was recorded would occur on any of the native or valued exotic on the Northern Hemisphere weeds Scrophularia au- species tested. riculata and Verbascum thapsus. These plant species were also highly palatable to the established biological Success of rearing method Using the rearing control agent, the buddleia leaf weevil C. japonicus method developed on cut stems within quarantine (Kay et al. 2008). There are other weevils from Europe (Gresham et al. 2002), offspring production during this (Cionus spp. Clairville, and other Cleopus spp.) that experiment was low even on B. davidii. An analysis of feed on Scrophularia, Verbascum and occasionally on the fate of all eggs per female for one entire breeding adventive Buddleja (Kay et al. 2005). In the United season revealed survival from egg to adult ranged Kingdom the only specialist lepidopteran to occasion- between 0 and 38% with a mean of 12% of eggs sur- ally feed on B. davidii is the mullein moth Cucullia viving to adult. Mean development time from egg to verbasci L., which normally has the same host range adult under the laboratory conditions was 66 days (SE as the figwort weevils (Owen and Whiteway 1980).